JS For Loop Inside a While Loop Returning Strange Results

Question

I am trying to split a string and combine it based on its index. A trivial example will be:

Input: "ABCABCABC" Output: "AAABBBCCC"

So I created a function that converts the string into an array pops off the elements into its appropriate array and hopefully combine it back to a string.

Here's the function:

function splitter(string, numSplit) {
  let splitHolder = [];
  let splitArr = string.split("");
  while (splitArr.length > 0) {
    for (let i = 0; i < numSplit; i++) {
      splitHolder[i] = splitHolder[i] === undefined
          ? [splitArr.shift()]
          : splitHolder[i].push(splitArr.shift());
      console.log(splitHolder);
    }
  }
}

Results for the console.log shows:

[ [ 'A' ] ]
[ [ 'A' ], [ 'B' ] ]
[ [ 'A' ], [ 'B' ], [ 'C' ] ]

which indicates the function is running okay at least on the first loop. However on the second pass of the for loop after it is checked by the while. I am getting this log:

[ 2, [ 'B' ], [ 'C' ] ]
[ 2, 2, [ 'C' ] ]
[ 2, 2, 2 ]

Which is very strange as I am still trying to push what is remaining of the array? Where did the numeric 2 come from?

Initially thought it was a scoping issue but it wasn't as the let is scoped for the whole function.

Also tried the array reduce function but am still getting the same numeric 2.

Array#push returns the new length of the array, and you're doing splitHolder[i] = splitHolder[i].push(...); Just use an if statement like everybody else. — Niet the Dark Absol
– Niet the Dark Absol, Commented Jul 14, 2020 at 14:27
Thanks for the comment of @NiettheDarkAbsol pointing me to the right direction on the what is causing the appearance of the number 2. It is indeed the length of the array. — Marka A
– Marka A, Commented Jul 14, 2020 at 14:39

Nina Scholz · Accepted Answer · 2020-07-14 14:33:56Z

1

You could take Array#concat instead of Array#push.

concat returns a new array and push the new length of the array.

function splitter(string, numSplit) {
    let splitHolder = [];
    let splitArr = string.split("");
    while (splitArr.length) {
        for (let i = 0; i < numSplit; i++) {
            splitHolder[i] = splitHolder[i] === undefined
                ? [splitArr.shift()]
                : splitHolder[i].concat(splitArr.shift());
        }
    }
    return splitHolder;
}


console.log(splitter('ABCABCABC', 3));

answered Jul 14, 2020 at 14:33

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Marka A Over a year ago

Thanks @Nina. Really missed that push return value. Leaned something new today.

Sheelpriy · Accepted Answer · 2020-07-14 14:53:21Z

0

Array.push() return new length of the array after push

 let arr =['A', 'B']

when you will push into this array.

arr.push('C') // return 3 . i.e. length of the array.

I think you don't want to push into splitHolder but concatenate the first element of splitArr .

function splitter(string, numSplit) {
  let splitHolder = [];
  let splitArr = string.split("");

  while (!!splitArr.length) {
    for (let i = 0; i < numSplit; i++) {
      splitHolder[i] = (splitHolder[i] === undefined)
          ? [splitArr.shift()]
          : splitHolder[i].concat(splitArr.shift());
      console.log(splitHolder);
    }
  }
 return splitHolder;
}

edited Jul 14, 2020 at 14:53

answered Jul 14, 2020 at 14:47

Sheelpriy

1,76517 silver badges28 bronze badges

Collectives™ on Stack Overflow

JS For Loop Inside a While Loop Returning Strange Results

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related